Utilization in optical code-division multiple-access networks.

摘要

This work investigates how O-CDMA exploits resources in multiwavelength optical fiber networks. For the first time, it examines this question fundamentally from the perspective of both transmission and network connectivity. Given the processing gain of O-CDMA, the spectral width of the transmitted signal may become appreciable relative to the spacing between adjacent channels. The assumption traditionally made in optical communications that these channels may be treated independently breaks down in this case. In this work, a figure of merit---the spectral utilization---together with an analytical framework are developed to treat the bandwidth of O-CDMA networks as a whole, rather than as a collection of independent segments.; The studies of O-CDMA with this spectral utilization metric suggest that the technology cannot compete with wavelength-division multiple-access (WDMA) at the physical layer taken in isolation; however, this is not the sole measure of the value of a network. Factors such as channel or receiver contention and the statistics of the traffic being transported do not manifest themselves in the physical layer yet are important factors in determining the performance of an optical network. A different figure of merit---the network utilization---is therefore used to compare and evaluate various O-CDMA and WDMA systems in a networking context.; In the process of studying O-CDMA through the spectral and network utilization, a number of specific original contributions are made: an impairment in O-CDMA networks---the spectral crosstalk---is studied for two different system configurations; a procedure is designed to evaluate the performance of O-CDMA signature sequences in realistic networking environments; and a technique is developed to allocate adaptively signature sequences which leads to an order of magnitude improvement in performance and provides a quality-of-service contract on the bit-error rate.; In local-area networks with a high traffic load, an O-CDMA system with static allocation of signature sequences is shown to have a higher network utilization than a competing WDMA scheme. It is demonstrated that by increasing the adaptability of the next generation of O-CDMA systems, the performance may be further improved. This work provides the tools-the analytical frameworks, figures of merit and mechanisms for adaptability-that may be used to design and evaluate these future O-CDMA systems.